The present invention relates in general to internally insulated panels and, in particular, to an adjustable joint for internally insulated panels particularly suitable for high temperature applications.
It is common in the steam generator field to use a box-type paneled structure comprising casing or plate material supported by external structural frame members to form internally insulated or packed panels for a heat recovery steam generator, abbreviated HRSG. As used herein, the term HRSG refers to a thermal structure used to extract the heat energy from turbine exhaust gas and use the energy to produce steam, typically for electric power generation.
FIG. 1 shows a cutaway illustration of such an HRSG 1. The HRSG 1 is provided with high temperature turbine exhaust gas 2, which can easily exceed 1000.degree. F., through an inlet flue 3. The exhaust gas 2 passes across an arrangement of heating surface and other components within the HRSG 1. The heating surface could be oriented substantially vertically, such as when a natural circulation design is employed, or substantially horizontally, such as when a forced circulation design is employed, or at some inclined angle to the horizontal as required. A box-type external structure or housing made of internally insulated side wall panels 4 partially surrounds this heating surface. To protect the insulation, an internal steel liner supported from the cold casing by nuts and welded studs is required. This configuration of liner, insulation, and casing is called a packed panel. Personnel protection considerations require sufficient insulation on these side wall panels 4 to achieve an external surface temperature of approximately 130.degree. F., eliminating the need to protect personnel in close proximity with the HRSG 1. Thermal expansions of the cold casing and support structure are also minimized by this configuration.
As shown in FIG. 1, a typical arrangement of components within the HRSG 1 might comprise: high pressure superheater 5; high pressure boiler 6; selective catalytic reduction and/or carbon monoxide reduction elements 7; intermediate pressure superheater 8; high pressure economizer 9; intermediate pressure boiler 10; high pressure economizer 11; intermediate pressure economizer 12; low pressure boiler 13; and condenser preheater 14. The gas 2 is then directed through an outlet transition housing 15 into a stack 16 for discharge into the atmosphere, by which point the exhaust gas has been reduced in temperature to approximately 200.degree. F. Located above the HRSG 1 heating surface and other components are a maintenance platform 17, structural steel 18, and penthouse 19, arranged around high, intermediate, and low pressure drums 6A, 10A, and 13A, respectively, and a deaerator 20.
Previous liner designs used in packed panel construction for such HRSG's require extensive field assembly and have been known to result in large internal gaps at the junctions between the packed panels after a period of time. These gaps produce hot spots on the outside casing at these locations.
FIG. 2 illustrates a known packed panel 30 comprising a cold pressure casing 32 which acts as the pressure boundary. Insulation 34 between a liner 36 and the cold pressure casing 32 drastically reduces the temperature of the turbine exhaust gas 2 passing along liner 36 through the thickness of packed panel 30. Collar studs 38 are welded to an inner surface of the cold pressure casing 32 and secure the liner 36 thereto by means of nuts 40 attached to the collar studs 38.
When constructing the box-type structure of packed panels 30 housing a heat recovery steam generator, it is common to have a junction or joint 42 between adjacent packed panels 30 as is shown in FIG. 2. The joint 42 used between adjacent insulated panels 30 requires extensive field assembly. Joint insulation 44 is required to be inserted between adjacent packed panels 30 and a joint liner 46 is provided to cover the joint insulation 44 and to connect the adjacent panels 30. A field weld 48 is provided at the cold pressure casing 32 between adjacent panels 30 to stabilize the joint 42.
Temporary bent liner plate corners have been used for shipping these packed panels. However, these corners had to be removed during field erection and were discarded. At the packed panel junctions, narrow, flat pieces of loose liner plate were field installed during erection to function as lap plates which protected the underlying insulation.
Illustrated in FIG. 3 is another known method for providing a joint 42 between adjacent packed panels 30, wherein permanent liner plates 36 are provided and bent at right angles to form a liner end 50. By bending the liner plate 36 to form a liner end 50, the adjacent panels 30 are allowed to be aligned adjacent to each other. The initial gap size between the liner ends 50 was a function of actual field fit up. However, after several boiler operating thermal cycles, the liner end 50 on one packed panel 30 assumes a thermally stable position relative to the insulation 34 and the liner end 50 of an adjacent packed panel 30. As shown in FIG. 4, each packed panel 30 has been known to undergo thermal expansion in direction 80 as shown. Subsequent thermal cycles result in compressed insulation 34, creating unpredictably sized gaps 52 between the liner ends 50 and a hot spot on the cold pressure casing 32 at that location.
Presently, there is no known device or method for providing a joint or junction for these packed panels used in heat recovery steam generators which requires minimum field assembly while eliminating the internal gaps and consequent hot spots formed between the packed panels during operation.